.TH std::iter_swap 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::iter_swap \- std::iter_swap

.SH Synopsis
   Defined in header <algorithm>
   template< class ForwardIt1, class ForwardIt2 >  (constexpr since C++20)
   void iter_swap( ForwardIt1 a, ForwardIt2 b );

   Swaps the values of the elements the given iterators are pointing to.

   If any of the following conditions is satisfied, the behavior is undefined:

     * a or b is not dereferenceable.
     * *a is not Swappable with *b.

.SH Parameters

   a, b             -             iterators to the elements to swap
.SH Type requirements
   -
   ForwardIt1, ForwardIt2 must meet the requirements of LegacyForwardIterator.

.SH Return value

   \fI(none)\fP

.SH Complexity

   Constant.

.SH Notes

   This function template models the semantics of the swap operation given by
   Swappable. That is, overloads of swap found by ADL and the fall back of std::swap
   are considered.

.SH Possible implementation

   template<class ForwardIt1, class ForwardIt2>
   constexpr //< since C++20
   void iter_swap(ForwardIt1 a, ForwardIt2 b)
   {
       using std::swap;
       swap(*a, *b);
   }

.SH Example

   The following is an implementation of selection sort in C++.


// Run this code

 #include <algorithm>
 #include <iostream>
 #include <random>
 #include <string_view>
 #include <vector>

 template<class ForwardIt>
 void selection_sort(ForwardIt begin, ForwardIt end)
 {
     for (ForwardIt it = begin; it != end; ++it)
         std::iter_swap(it, std::min_element(it, end));
 }

 void println(std::string_view rem, std::vector<int> const& v)
 {
     std::cout << rem;
     for (int e : v)
         std::cout << e << ' ';
     std::cout << '\\n';
 }

 template<int min, int max>
 int rand_int()
 {
     static std::uniform_int_distribution dist(min, max);
     static std::mt19937 gen(std::random_device{}());
     return dist(gen);
 }

 int main()
 {
     std::vector<int> v;
     std::generate_n(std::back_inserter(v), 20, rand_int<-9, +9>);

     std::cout << std::showpos;
     println("Before sort: ", v);
     selection_sort(v.begin(), v.end());
     println("After sort:  ", v);
 }

.SH Possible output:

 Before sort: -9 -3 +2 -8 +0 -1 +8 -4 -5 +1 -4 -5 +4 -9 -8 -6 -6 +8 -4 -6
 After sort:  -9 -9 -8 -8 -6 -6 -6 -5 -5 -4 -4 -4 -3 -1 +0 +1 +2 +4 +8 +8

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

     DR    Applied to      Behavior as published              Correct behavior
   LWG 187 C++98      it was unspecified whether swap the effect is equivalent to
                      is used                         swap(*a, *b)

.SH See also

   swap        swaps the values of two objects
               \fI(function template)\fP
   swap_ranges swaps two ranges of elements
               \fI(function template)\fP
   iter_swap   swaps the objects pointed to by two adjusted underlying iterators
   (C++20)     \fI(function template)\fP
   iter_swap   swaps the objects pointed to by two underlying iterators
   (C++20)     \fI(function template)\fP
   iter_swap   swaps the values referenced by two dereferenceable objects
   (C++20)     (customization point object)
